Field of the Invention
The present invention relates to a power conversion device, and particularly relates to a power conversion device including a device that controls discharge of electric charges accumulated in a capacitor.
Description of Related Art
A power conversion device includes a boost converter that boosts a DC voltage supplied from a chargeable/dischargeable DC power source, a primary smoothing capacitor that smooths a voltage between the DC power supply and the boost converter, an inverter that converts a high-pressure DC voltage outputted from the boost converter into an AC voltage and a secondary smoothing capacitor that smooths a voltage between the boost converter and the inverter, having a function of supplying the AC voltage outputted from the inverter to a motor.
In a vehicle provided with the power conversion device, electric charges accumulated in the secondary smoothing capacitor are discharged immediately when the vehicle collides or an engine is stopped for preventing electrical shock. The discharge is performed by three-phase ON control of the inverter so that all switching devices in an upper arm and all switching devices in a lower arm in plural switching devices of the inverter are in an ON state. However, a voltage of the secondary smoothing capacitor is increased due to an induced voltage from the motor when the motor is rotating at the time of the control, therefore, a discharging time may be elongated and a temperature of the inverter may be increased to a limit temperature of driving.
Accordingly, in the description of Patent Literature 1, three-phase ON control is stopped when the temperature of an inverter reaches a threshold value or more obtained by subtracting an estimated increased temperature in the discharge control from the limit temperature of driving during execution of the three-phase ON control for suppressing voltage increase due to the induced voltage from the motor.
However, in the technique proposed in Patent Literature 1, there is a problem that an action for a case where it is difficult to detect the rotation speed of the motor is not considered and thus it is difficult to execute the discharge control when the rotation speed is not detected. There is also a problem that gradual reduction of temperature and elongated execution time of discharge control occuring after the three-phase ON control is stopped are not considered, furthermore, there is a problem that determination for stopping the three-phase ON control is made in an early stage as a threshold for determining the stop of the three-phase ON control is set to a lower value than the limit temperature of driving.
[Patent Literature 1] JP-A-2016-111754